1. Field of the Invention
This invention relates to document printers and particularly to space efficient document printers which can run without operator intervention for extended periods of time.
2. Description of Related Art
High speed document printers capable of print rates in excess of 200 pages per minute using xerographic and inkjet printing engines have been developed. As printer throughput rates increase, a larger percentage of operator time is spent loading copy sheets into and unloading printed output from the machine. To overcome this limitation, load-while-run features have been developed to allow the printer to continue operating while paper is loaded and output is unloaded from the printer. One such arrangement is illustrated in U.S. Pat. No. 5,096,181. In general, this system utilizes two sheet stack receiver elements, one of which is positioned in an input position for stack feeding or an output position for stack formation. The second receiver is movable and can be loaded or unloaded by an operator while sheet feeding or stack formation is taking place at the first receiver. When the stack of copy sheets in the first receiver is exhausted (in the copy sheet input stage) or completed (in the copy sheet output stage) a transfer mechanism moves a new stack of copy sheets to the first receiver from the second receiver or moves a completed stack of printed sheets from the first receiver to the second receiver. In general, this system is relatively slow and makes inefficient use of feeder and elevator hardware because the transfer operation is relatively slow. This causes a significant interruption in the operation of the printer and reduces throughput. Also, the receivers are enclosed within the printer and it is difficult to quickly visualize when attention to the second receiver is necessary. This is disadvantageous when it is desirable to have a large number of printers attended by a minimum number of operators, as production is interrupted if the printers must stop because of a lack of supply of copy sheets or the need to remove copy output.